Dynamoelectric machine cooling arrangement

ABSTRACT

A dynamoelectric machine includes a rotor, a stator and a housing supporting the rotor and stator. There are openings in the housing for flow of air through the housing toward one end. A cover, mounted to the housing, forms a chamber positioned axially beyond the one end of the rotor and stator and extending radially beyond the periphery of the housing. The cover has a plurality of exit openings positioned around the radial edge of the chamber. A centrifugal fan is mounted to the rotor shaft within the chamber and extends radially beyond the periphery of the housing. The fan draws air through the housing into the chamber and discharges it from the chamber in a generally radial direction through the exit openings.

[ 1 March 6, 1973 t v Unite States atent n 1 Dochterman I DYNAMOELECTRICMACHINE COOLING ARRANGEMENT [75] Inventor: Richard W. Dochterman, FortWayne, Ind.

[73] Assignee: General Electric Company, Fort Wayne, Ind.

[22] Filed: May24,197l

[21] App1.No.:146,134

[52] U.S.Cl ..3110/89,310/62 [51] Int. Cl. ..1-l02lk 5/00 [58]FieldofSeai-ch ..310/52,58,62,63,54,85, 310/89 [5 6] References CitedUNITED STATES PATENTS 2,100,020 11/1937 Andrews ..3l0/63 3,437,8554/1969 Laing ..310/62 3,512,024 5/1970 Papa ..3lO/63 3,395,644 8/1968Grebel ..3lO/58 2,032,552 3/1936 Seyfried ..310/62 iii FOREIGN PATENTSOR APPLICATIONS 287,441 2/1966 Australia ..3l0/63 Primary Examiner-R.Skudy Attorney-John M. Stoudt, Radford M. Reams, Ralph E. Krisher, Jr.,Joseph B. Forman, Frank L. Neuhauser and Oscar B. Waddell 5 7] ABSTRACTA dynamoelectric machine includes a rotor, a stator and a housingsupporting the rotor and stator. There are openings in the housing forflow of air through the housing toward one end. A cover, mounted to thehousing, forms a chamber positioned axially beyond the one end of therotor and stator and extending radially beyond the periphery of thehousing. The cover has a plurality of exit openings positioned aroundthe radial edge of the chamber. A centrifugal fan is mounted to therotor shaft within the chamber and extends radially beyond the peripheryof the housing. The fan draws air through the housing into the chamberand discharges it from the chamber in a generally radial directionthrough the exit openings.

10 Claims, 2 Drawing Figures ZJI PATENTED 61975 FIGZ DYNAMOEIJECTRICMACHINE COOLING ARRANGEMENT BACKGROUND OF THE INVENTION This inventionrelates to dynamoelectric machines, such as electric motors forinstance. More particularly, it relates to improved arrangements forcooling such machines.

One of the important factors in determining what 1 electric motor to usein any particular application is the operating temperature of each ofthe motors considered. For any given motor core size, that is givenstator and rotor size, the higher the horsepower output of the motor thegreater will be the heat loss. This causes the operating temperature ofthe motor to tend to rise to higher levels. Many times the limitation ofsuch operating temperature necessitates the use of larger or moreexpensive motor designs than would otherwise be required. For instancethere are many applications now met by using distributed wound motorswhich could be met by an equivalent sized shaded pole motor, except forthe operating temperature requirements. Generally speaking shaded polemotors of a given size are cheaper to manufacture than distributed woundmotors of a similar size. However shaded pole motors have greaterelectrical losses, which are manifest in greater heat generation in themotors.

For a given core size the horsepower rating of a motor may be increasedby increasing the number of windings. However, efforts to increase motorratings in this manner are limited by the operating temperature as morewindings generate more heat that must be dissipated.

Many attempts have been made to cool motors. One approach is to providea fan which is powered by the rotor and forces air over and/or throughthe motor. This tends to dissipate the heat generated by electricallosses of the motor and provides the motor with a lower steady stateoperating temperature. Cooling fans have had mixed results. Some of theproblems include providing sufficient air volume, optimum air flowdirection and adequate shielding of the fan when mounted exteriorly ofthe motor housing.

Therefore it is an object of the present invention to provide animproved dynamoelectric machine cooling arrangement.

It is a further, more specific object of the present invention toprovide such an improved cooling arrangement which results in enhancedcooling air flow.

It is yet a further object of the present invention to provide animproved cooling arrangement of the type in which the fan is mountedexteriorly of the motor housing. 1

Still another object of the present invention is to provide an improvedfan cover for use with a dynamoelectric machine having a fan mountedexteriorly of the housing.

SUMMARY OF THE INVENTION In carrying out the present invention, in oneform thereof, I provide a dynamoelectric machine including a rotor and astator. A housing, for supporting the rotor and stator for relativerotation, includes a peripheral wall and a pair of end shields, each ofthe end shields substantially closes a corresponding end of theperipheral wall and has openings therein to allow flow of air throughthe housing. A shaft is mounted to the rotor and extends through atleast one of the end shields. A cover is mounted to the housing anddefines a chamber positioned axially beyond the one end shield andextending radially beyond the peripheral wall. The cover further definesa plurality of exit openings positioned about the radially outer portionof the chamber. A centrifugal fan is mounted to the shaft within the 0chamber and extends radially beyond the peripheral wall of the housing.The fan is adapted to draw air into the chamber through the housing andto discharge air in a generally radial manner through the openings inthe cover.

The above mentioned and other features and objects of this invention, aswell as the manner of obtaining them will be more apparent, and theinvention itself will be better understood by reference to the followingdescription, taken in conjunction with the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a somewhat simplified sideelevational view of a dynamoelectric machine cooling arrangement inaccordance with one form of the present invention, the view being partlybroken away and partly in section for purposes of illustration; and

FIG. 2 is a partial bottom plan view of the fan cover incorporated inthe motor cooling arrangement of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Turning now to the drawingthere is shown therein a dynamoelectric machine cooling arrangement asutilized with a shaded pole motor 10, as the illustrated coolingarrangement is particularly effective with that type of motor. The motorIt) includes a stationary structure or stator 11. The stator includes astator core 12 formed by a plurality of laminations of relatively thinmagnetic material shaped to provide spaced apart teeth 12a with awinding 13 provided about each tooth and extending through the slot 14on each side of each tooth. lPins or retaining members 15 hold each ofthe windings 13 in place within their corresponding slots and radiallyoutwardly of the central bore 16 provided through the stator core. Itwill be understood that with shaded pole motors the individual teeth orpoles have a salient shape to provide slots which, in a circumferentialdirection, normally are somewhat larger than the windings receivedtherein so that the sides of the windings 113 do not fill the slots 14.

A rotor 18 is received in the bore 16 and is mounted on a shaft 19. Theillustrated rotor 18 is of the squirrel cage type, being provided with asquirrel cage winding 20. A plurality of small fins or blades 21 arecast integrally with the rotor at each end thereof.

The motor also includes a housing formed by a generally cylindricalmember 22, which defines a peripheral wall tightly encompassing andsupporting the stator core 12, and a pair of end shields 23 and 24. Eachof the end shields 23, 24 substantially closes one end of the peripheralwall 22. A number of bolts 25 extend between the end shields 23, 24 soas to clamp the housing members together to form a unitary structure.The end shields 23, 24 form supports for bearings 26a and 26brespectively and the bearings, in turn, rotatably support the rotorshaft 19. Thus the housing supports the stator and the rotor forrelative rotary motron.

The end shields are provided with mating openings 27 and 28 which arepositioned generally in axial alignment with the slots 14 in the statorcore. This provides a path for air flow generally axially through themotor. Additionally the peripheral wall or cylindrical member 22 isprovided with a number of openings 29 adjacent the end shield 23 toprovide for additional air flow through the motor. Cooling air can enterthe house through openings 27 and 29, flow generally axially through thehousing, primarily through the stator slots 14, and then exit from thehousing through openings 28. The openings 27 and 28 preferably arealigned with the openings 14 between adjacent stator teeth. Such analignment properly directs the stream of air and results in greater airflow.

In the exemplification the shaft 19 extends completely through each ofthe bearings 26a, 26b to provide exposed shaft ends 19a and 19b.Conventionally the shaft end 19a is connected to a device or mechanismto be driven by the motor such as a sump pump for instance. Acentrifugal fan 30 is attached to the shaft end 1%. To this end, thecentrifugal fan 30 includes an end plate 31 and a hub 32. The hub 32fits tightly about and is connected to the shaft end 1911 by means of aset screw 33 which is threaded into the hub 32 and rides in an annularrecess 34 in the shaft end 19b. Thus the centrifugal fan 30 rotates withthe rotor shaft 19. The end plate 31 extends generally radiallyoutwardly from the hub 32 and is provided with a number of vanes orblades 35. Each of the blades 35 runs generally radially along the endplate 31 and projects axially of the motor from the end plate 31 backtowards the end shield 24. The end plate 31 and the blades 35 extendradially beyond the outer periphery of the cylindrical member orperipheral wall 22. The blades 35 are provided with notches 36 so thatblades may clear the ends of bolts 25 as they rotate in close proximityto the end shield 24.

A fan cover or housing 40 is mounted to the motor housing and enclosesthe fan 35. The cover 40 includes a first wall portion 41 which has across section complimentary to and slightly larger than the peripheralwall 22 of the motor housing. In the exemplification, in which theperipheral wall 22 is cylindrically shaped, the first wall portion 41 iscylindrical in cross section, has a slightly larger diameter than theoutside diameter of the peripheral wall 22 and extends axially of themotor in an overlapping relationship with the peripheral wall 22. Thecover 40 also includes a second wall portion 42 which is generallyparallel to the peripheral wall 22 and in axial alignment with the fan30. The wall portion 42 is of a slightly greater diameter than the fan30 and is perforated so as to provide a number of openings 43 which aredisposed generally radially with respect to the motor. A third,imperforate wall portion 44 joins the first wall portion 41 and thesecond wall portion 42 while a fourth or end wall portion 45 closes theend of the second wall portion of the cover 40 remote from the motor.

The cover 40, together with the motor housing, defines a chamber 46positioned axially beyond the end shield 24 and extending radiallybeyond the peripheral wall 22. The openings 43 provide generallyradially disposed exit openings for the chamber 46.

In the exemplification the first wall portion 41 is provided with anumber of mounting members in the form of tabs 47 which extend inwardlytherefrom and are received in corresponding openings 48 in theperipheral wall 22 of the motor housing. Each of the tabs includes aradially inward portion 49 positioned between a pair of mountingsurfaces 50. When the wall portion 41 is placed about the peripheralwall 22, the radial inward portion 49 of each tab is received in acorresponding opening 48 of wall 22 and the mounting surfaces 50 engageadjacent areas of peripheral wall 22. This positions the cover 40 inplace about the fan 35 and also serves to hold the first wall portion 41in spaced relation to the peripheral wall 22 so that a passageway 51 isformed around the circumference of the wall 22 for entry of air into thechamber 46.

Referring now to FIGS. 1 and 2 together, it will be seen that the cover40 is formed by a pair of identically shaped cover sections 55 and 56.The ends of first and second wall portions 41, 42 of both cover sections55, 56 are formed with lugs 57 and 58 respectively. The lugs 57, 58 areprovided with alternate pins 59 and mating recesses 60. Similarly a pin59 and a slot (not shown) are provided in each of the top wall portions45. An inwardly projecting auxiliary tab 61 is provided in the firstwall portion of each cover section 55, 56 adjacent each lug 58.

In order to assemble the cover 40 each cover section is placed about themotor housing and fan with its mounting members 47 being received incorresponding openings 48 in the peripheral wall 22 of the housing. Thepins 59 are received in corresponding recesses 60 to precisely align thetwo cover sections relative to one another with mating pairs of lugs 57,58 in engagement. Thereafter a spring clip 62 is mounted about eachmating pair of lugs 57, 58 to firmly connect the two sections into acomplete cover. The auxiliary tabs 61 engage the peripheral wall 22 ofthe housing to firmly support the area of the joint between the twocover sections. The cover sections can be mechanically attached orfirmly connected by any-one of a number of other means such as, forinstance, screws, adhesive or sonic welding. Clips 62 are shown in theexemplification as they are quickly and easily mounted and, at the sametime, provide a firm connection.

Each of the cover sections in the exemplification is exactly like theother cover section and includes half of each of the first, second,third and fourth wall portions. This enables the use of one set of moldsto make all of the required cover sections and facilitates properassembly to form the covers. It will be understood, however, that othercomplimentary sections may be used in forming the cover. By formingcover in sections it is possible to easily mount the cover about themotor and the fan so as to have the first wall portion 41 closelyoverlie the peripheral wall 22 while the second wall portion closelyoverlies the fan 30. Such a housing design provides optimally directed,enhanced air flow and is relatively strong. At the same time I am ableeasily to mold the cover sections from low cost thermoplastic materialssuch as polypropylene, nylon or ABS (acrylonitrile, butadiene andstyrene). One form of ABS is sold by Mabon Chemical Division of Borg-Warner Corporation under the name Cycolac.

Considering now particularly FIG. l and assuming the windings 13 areenergized to cause rotation of rotor 18, the centrifugal fan 30 rotateswith the rotor 18. This draws air into the housing through the openings27 and 29, then axially through the housing with some of the air passingthrough the bore 16 between the rotor and the stator while a largerportion of the air passes through the slots 14 around the side turnportions of the windings. The air exits from the housing through theopenings 28 and end shield 24 into the chamber 46. Additionally air isdrawn generally axially along the outer surface of the peripheral wall22, and through the passageway 51 into the chamber 46. The centrifugalfan 30 also functions to expel the air generally radially from thechamber 46 through the exit openings 43.

The exemplification illustrates the cover 40 with the first wall portion41 slightly larger than the peripheral wall 22 of the motor housing toform the passageway 51 as the exemplification motor is a four pole motorof the shaded pole type in which the slots 14 normally are notsufficiently large to allow sufficient air flow through the motor forthe most effective cooling. In other embodiments, as with a two polemotor of the shaded pole type for example, the slots in such a motorcorresponding to slots 14 are enough larger than the windings to allowsufficient air flow through the motor for optimum cooling. In such anexemplification the first wall portion ll of the fan cover preferablywould be mounted in firm engagement with the peripheral wall 22 of themotor housing so that all the air is drawn through the housing ratherthan part of it being drawn around the outer circumference of thehousing.

In either event the exit openings 43 are distributed about the outercircumference of the chamber 46 so that the air exiting from the chamber46 moves generally radially away from the motor and does not tend to berecirculated about the motor as such recirculation would reduce thecooling effect of the air.

It also will be understood that with motors of the unit bearing type anend shield corresponding to end shield 24 would not be needed forpurposes of supporting a bearing since such motors have only one bearingsupported from one end. In such a case the end shield between thecentrifugal fan and the stator and rotor may be omitted. The centrifugalfan then would be mounted to just clear the end of the housingperipheral wall and the winding end turns. In such a construction thefan cover would also serve to close off the end of the motor.

. While, in accordance with the Patent Statutes, I have shown anddescribed what at present are considered to be the preferred embodimentsof this invention, it should be apparent to those skilled in the artthat changes and modifications may be made in the disclosed apparatuswithout actually departing from the true spirit and scope of thisinvention and it is therefore aimed in the appended claims to cover allequivalent variations that fall within the true spirit and scope of theinvention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

ll. A dynamoelectric machine, including:

a. a rotor and a stator;

b. a housing supporting said rotor and stator for relative rotation;said housing including a peripheral wall and a pair of end shields, eachof said end shields substantially closing a corresponding end of saidperipheral wall;

c. at least one of said end shields having openings therein forpromoting air flow through said housing;

. a shaft mounted to said rotor and extending axially beyond said atleast one of said end shields;

e. a cover mounted to said housing; said cover including a firstgenerally axially extending wall at least partly defining a fan chamberpositioned axially beyond said at least one of said end shields andextending radially outwardly, and a second substantially imperforatewall overlying the fan chamber; said cover further defining a pluralityof exit openings positioned about the radially outer portion of saidchamber; and

f. a centrifugal fan mounted to said shaft within said fan chamber, saidfan extending radially outwardly and being operative to draw air intothe fan chamber through said housing and to discharge air in a generallyradial manner through the exit openings in said cover.

2. A dynamoelectric machine as set forth in claim 1 wherein: means,including said cover, forms passageway for entry of air into saidchamber exteriorly of said housing so that said fan also draws airgenerally axially along the exterior of said peripheral wall into saidchamber.

3. A dynamoelectric machine, including: a rotor and a stator; a housingsupporting said rotor and stator for relative rotation; said housingincluding a peripheral wall and a pair of end shields, each of said endshields substantially closing a corresponding end of said peripheralwall; each of said end shields having openings therein to allow flowofair through said housing; a shaft mounted to said rotor and extendingthrough at least one of said end shields; a cover mounted to saidhousing; said cover defining a chamber positioned axially beyond said atleast one of said end shields and extending radially beyond saidperipheral wall; said cover further defining a plurality of exitopenings positioned about the radially outer portion of the chamber; acentrifugal fan mounted to said shaft within said chamber, said fanextending radially beyond said peripheral wall and being adapted to drawair into the chamber through said housing and to discharge air in agenerally radial manner through the exit openings in said cover; means,including the cover, forming at least one passageway for entry of airinto said chamber exteriorly of said housing so that said fan also drawsair generally axially along the exterior of said peripheral wall intosaid chamber; said cover including: a first wall portion overlapping andspaced radially outward of said peripheral wall; a second wall portionextending generally axially of said machine and in radial alignment withsaid fan, said second wall portion being provided with the exitopenings; and a substantially imperforate third wall portion joiningsaid first and second wall portions.

4. A dynamoelectric machine as set forth in claim 3 wherein: saidperipheral wall is provided with a plurality of mounting openings; saidfirst wall portion includes a plurality of inwardly extending, integralmounting members; each of said mounting members being received in acorresponding one of the openings in said peripheral wall and engagingsaid peripheral wall for positively positioning said first wall portionabout said peripheral wall.

5. A dynamoelectric machine as set forth in claim 1 wherein: the regionof said peripheral wall remote from said one end shield is provided withair inlet openings for enhanced cooling air flow through said housing.

6. A dynamoelectric machine, including:

a. a rotor and a stator;

b. a housing supporting said rotor and stator for relative rotation,said housing including a peripheral wall;

c. said housing defining openings therein for flow of air through saidhousing toward one end thereof;

d. a shaft mounted to said rotor and extending axially beyond at leastsaid one end of said rotor and stator;

e. a cover mounted to said housing and defining a fan chamber positionedaxially beyond said one end of said rotor and stator; said coverextending radially outwardly and further defining a plurality of exitopenings positioned about the radially outer portion of the fan chamber;and

f. a centrifugal fan mounted to said shaft within the fan chamber; saidfan overlying at least some of the openings defined by the housing withthe at least some of the openings establishing an unrestricted path forair flow from said housing to the fan chamber, said fan extendingradially outwardly and being operative to draw air into the fan coverthrough the at least some of the openings from the interior of saidhousing and to discharge air generally radially through the exitopenings in said cover.

7. For use with a dynamoelectric machine including a housing having aperipheral wall, a shaft extending axially beyond one end of theperipheral wall and a centrifugal fan mounted on the shaft exteriorly ofthe one end of the peripheral wall; a fan cover comprising:

a. a first wall portion having a cross section of the housing foroverlapping mounting about the one end of the peripheral wall;

b. a second wall portion generally parallel to the peripheral wall whensaid cover is mounted to the dynamoelectric machine and defining aplurality of exit openings therein;

c. a plurality of inwardly extending mounting members spaced around saidfirst wall portion for receipt in corresponding openings in theperipheral wall;

. said mounting members being resiliently movable relative to otherportions of the cover so that the mounting members are movable along theoutside of the peripheral wall into interfitting relationship withcorresponding openings in the peripheral wall; the mounting membersholding the first wall portion in overlapping relation to the peripheralwall.

8. For use with a dynamoelectric machine including a housing having aperipheral wall, a shaft extending axially beyond at least one end ofthe peripheral wall and a centrifugal fan mounted on the shaftexteriorly of the at least one end of the peripheral wall; a fan covercomprising: a first wall portion having a cross section complimentary toand slightly lar er I than the peripheral wa of the housing for overapping mounting about the at least one end of the peripheral wall; asecond wall portion generally parallel to the peripheral wall when saidcover is mounted to the dynamoelectric machine and defining a pluralityof exit openings therein; a plurality of inwardly extending mountingmembers spaced around said first wall portion for receipt incorresponding openings in the peripheral wall; said first wall portionbeing sufficiently resilient to allow said mounting members to movealong the outside of the peripheral wall until they are aligned withcorresponding openings and thereafter to restrain said mounting membersin the corresponding openings with said first wall portion overlappingspaced outwardly of the peripheral wall; said second wall portion beingof a larger diameter than said first wall portion; and said cover alsoincluding a substantially imperforate, generally radially disposed thirdwall portion joining said first and second wall portions.

9. A fan cover as set forth in claim 8 further including a fourth wallportion closing the end of said second wall portion remote from saidfirst wall portion.

10. A fan cover as set forth in claim 9 wherein said cover is composedofa plurality of substantially similar, separate sections mechanicallyattached to one another, each of said sections forming part of each ofsaid wall portions.

1. A dynamoelectric machine, including: a. a rotor and a stator; b. ahousing supporting said rotor and stator for relative rotation; saidhousing including a peripheral wall and a pair of end shields, each ofsaid end shields substantially closing a corresponding end of saidperipheral wall; c. at least one of said end shields having openingstherein for promoting air flow through said housing; d. a shaft mountedto said rotor and extending axially beyond said at least one of said endshields; e. a cover mounted to said housing; said cover including afirst generally axially extending wall at least partly defining a fanchamber positioned axially beyond said at least one of said end shieldsand extending radially outwardly, and a second substantially imperforatewall overlying the fan chamber; said cover further defining a pluralityof exit openings positioned about the radially outer portion of saidchamber; and f. a centrifugal fan mounted to said shaft within said fanchamber, said fan extending radially outwardly and being operative todraw air into the fan chamber through said housing and to discharge airin a generally radial manner through the exit openings in said cover. 1.A dynamoelectric machine, including: a. a rotor and a stator; b. ahousing supporting said rotor and stator for relative rotation; saidhousing including a peripheral wall and a pair of end shields, each ofsaid end shields substantially closing a corresponding end of saidperipheral wall; c. at least one of said end shields having openingstherein for promoting air flow through said housing; d. a shaft mountedto said rotor and extending axially beyond said at least one of said endshields; e. a cover mounted to said housing; said cover including afirst generally axially extending wall at least partly defining a fanchamber positioned axially beyond said at least one of said end shieldsand extending radially outwardly, and a second substantially imperforatewall overlying the fan chamber; said cover further defining a pluralityof exit openings positioned about the radially outer portion of saidchamber; and f. a centrifugal fan mounted to said shaft within said fanchamber, said fan extending radially outwardly and being operative todraw air into the fan chamber through said housing and to discharge airin a generally radial manner through the exit openings in said cover. 2.A dynamoelectric machine as set forth in claim 1 wherein: means,including said cover, forms passageway for entry of air into saidchamber exteriorly of said housing so that said fan also draws airgenerally axially along the exterior of said peripheral wall into saidchamber.
 3. A dynamoelectric machine, including: a rotor and a stator; ahousing supporting said rotor and stator for relative rotation; saidhousing including a peripheral wall and a pair of end shields, each ofsaid end shields substantially closing a corresponding end of saidperipheral wall; each of said end shields having openings therein toallow flow of air through said housing; a shaft mounted to said rotorand extending through at least one of said end shields; a cover mountedto said housing; said cover defining a chamber positioned axially beyondsaid at least one of said end shields and extending radially beyond saidperipheral wall; said cover further defining a plurality of exitopenings positioned about the radially outer portion of the chamber; acentrifugal fan mounted to said shaft within said chamber, said fanextending radially beyond said peripheral wall and being adapted to drawair into the chamber through said housing and to discharge air in agenerally radial manner through the exit openings in said cover; means,including the cover, forming at least one passageway for entry of airinto said chamber exteriorly of said housing so that said fan also drawsair generally axially along the exterior of said peripheral wall intosaid chamber; said cover including: a first wall portion overlapping andspaced radially outward of said peripheral wall; a second wall portionextending generally axially of said machine and in radial alignment withsaid fan, said second wall portion being provided with the exitopenings; and a substantially imperforate third wall portion joiningsaid first and second wall portions.
 4. A dynamoelectric machine as setforth in claim 3 wherein: said peripheral wall is provided with aplurality of mounting openings; said first wall portion includes aplurality of inwardly extending, integral mounting members; each of saidmounting members being received in a corresponding one of the openingsin said peripheral wall and engaging said peripheral wall for positivelypositioning said first wall portion about said peripheral wall.
 5. Adynamoelectric machine as set forth in claim 1 wherein: the region ofsaid peripheral wall remote from said one end shield is provided withair inlet openings for enhanced cooling air flow through said housing.6. A dynamoelectric machine, including: a. a rotor and a stator; b. ahousing supporting said rotor and stator for relative rotation, saidhousing including a peripheral wall; c. said housing defining openingstherein for flow of air through said housing toward one end thereof; d.a shaft mounted to said rotor and extending axially beyond at least saidone end of said rotor and stator; e. a cover mounted to said housing anddefining a fan chamber positioned axially beyond said one end of saidrotor and stator; said cover extending radially outwardly and furtherdefining a plurality of exit openings positioned about the radiallyouter portion of the fan chamber; and f. a centrifugal fan mounted tosaid shaft within the fan chamber; said fan overlying at least some ofthe openings defined by the housing with the at least some of theopenings establishing an unrestricted path for air flow from saidhousing to the fan chamber, said fan extending radially outwardly andbeing operative to draw air into the fan cover through the at least someof the openings from the interior of said housing and to discharge airgenerally radially through the exit openings in said cover.
 7. For usewith a dynamoelectric machine including a housing having a peripheralwall, a shaft extending axially beyond one end of the peripheral walland a centrifugal fan mounted on the shaft exteriorly of the one end ofthe peripheral wall; a fan cover comprising: a. a first wall portionhaving a cross section of the housing for overlapping mounting about theone end of the peripheral wall; b. a second wall portion generallyparallel to the peripheral wall when said cover is mounted to thedynamoelectric machine and defining a plurality of exit openingstherein; c. a plurality of inwardly extending mounting members spacedaround said first wall portion for receipt in corresponding openings inthe peripheral wall; d. said mounting members being resiliently movablerelative to other portions of the cover so that the mounting members aremovable along the outside of the peripheral wall into interfittingrelationship with corresponding openings in the peripheral wall; themounting members holding the first wall portion in overlapping relationto the peripheral wall.
 8. For use with a dynamoelectric machineincluding a housing having a peripheral wall, a shaft extending axiallybeyoNd at least one end of the peripheral wall and a centrifugal fanmounted on the shaft exteriorly of the at least one end of theperipheral wall; a fan cover comprising: a first wall portion having across section complimentary to and slightly larger than the peripheralwall of the housing for overlapping mounting about the at least one endof the peripheral wall; a second wall portion generally parallel to theperipheral wall when said cover is mounted to the dynamoelectric machineand defining a plurality of exit openings therein; a plurality ofinwardly extending mounting members spaced around said first wallportion for receipt in corresponding openings in the peripheral wall;said first wall portion being sufficiently resilient to allow saidmounting members to move along the outside of the peripheral wall untilthey are aligned with corresponding openings and thereafter to restrainsaid mounting members in the corresponding openings with said first wallportion overlapping spaced outwardly of the peripheral wall; said secondwall portion being of a larger diameter than said first wall portion;and said cover also including a substantially imperforate, generallyradially disposed third wall portion joining said first and second wallportions.
 9. A fan cover as set forth in claim 8 further including afourth wall portion closing the end of said second wall portion remotefrom said first wall portion.